The invention relates to a tool for preforming a metallic starter tube section for subsequent internal high pressure forming.
The invention also relates to a method for producing such a tool.
The invention further relates to a method for producing a tube-like component by internal high pressure forming.
In internal high pressure forming (IHF), an essentially metallic tube, referred to below as the starter tube section, is formed into a tube-like component (IHF component) by the application of a high internal pressure. The expression “a tube” is generally understood to denote a longitudinally extending hollow body having a closed tube casing made from a metallic material. The starter tube section is inserted for this purpose into the cavity (engraving) of a shaping IHF tool and is opened out essentially transversely to the longitudinal axis by use of a fluid (e.g. a water/oil emulsion) introduced into the interior, wherein the tube casing of the starter tube section is pressed against the cavity wall and is shaped accordingly in the process.
Frequently, and in particular in the case of a complex shape of the IHF component, preforming is initially necessary, wherein a preformed starter tube section for the subsequent internal high pressure forming is produced from the starter tube section in the IHF tool. Preforming has a considerable influence on the following internal high pressure forming and on the quality of the IHF component.
Various procedures and apparatuses for preforming are familiar from the prior art, in respect of which reference is made to patent specifications DE 10 2006 028 099 A1, DE 101 48 451 C2, DE 199 46 010 B4 and EP 0 195 157 B1.
The object of the invention is to provide a tool for preforming a metallic starter tube section, which permits an optimal distribution of the tube material with a view to subsequent internal high pressure forming. The object of the invention is further to provide an optimized method for the production of a tube-like IHF component.
This and other objects are achieved by, in accordance with embodiments of the invention, providing a tool for preforming a tube for subsequent internal high pressure forming, and methods for producing such a tool and for producing an internal high pressure formed component.
A tool according to the invention for preforming a metallic starter tube section for subsequent internal high pressure forming for the production of a tube-like IHF component has a plurality of tool components with the ability to move relative to one another, which between them delimit (at least) one cavity for receiving and forming the starter tube section. According to the invention, it is proposed that the cavity has a contour which is both derived from the shape (or geometry) of the IHF component to be produced and is adapted to the circumference of the starter tube section to be formed, such that each cavity cross section of this cavity perpendicular to a cavity longitudinal axis predefined by the starter tube section conforms to the cross-sectional shape of the IHF component cross section in the same position (relative to the longitudinal axis), reduced in its cross-sectional circumference to exactly the circumference of the starter tube section.
In other words, this means that the cross-sectional shape of each cavity cross section, along a cavity longitudinal axis predetermined by the starter tube section, corresponds to the reduced cross-sectional circumference of the cross section of the IHF component in the same position or in the same location relative to the longitudinal axis, wherein the cross-sectional circumference of each cavity cross section in each case conforms exactly to the circumference of the starter tube section, however.
The cross-sectional geometry of a cross section consists essentially of the shape or the cross-sectional shape and the circumference or the cross-sectional circumference, from which an appropriate area or cross-sectional area results.
The cavity of the tool according to the invention has a cavity longitudinal axis that is predetermined by the starter tube section, wherein the cavity longitudinal axis is essentially identical to the longitudinal axis of an inserted starter tube section. It is proposed according to the invention that the respective cavity cross section at every point or at every location on this cavity longitudinal axis exhibits a reduced cross-sectional shape of the IHF component to be produced relative to an IHF component cross section at the same point on the longitudinal axis, wherein the respective cross-sectional circumference corresponds exactly to the circumference of the starter tube section, however. The circumference of the starter tube section thus determines at each point the scaling factor for the reduction of the cross-sectional shape of the respective IHF component cross-section (in which case the scaling factor must be ≤1). Compared with the IHF component to be produced or compared with the cavity of the shaping IHF tool, the cavity of the tool according to the invention thus exhibits a variable offset along its cavity longitudinal axis, wherein the respective offset dimension is obtained from the scaling factor.
Each cross section of a starter tube section that has been preformed with this tool has the same distance or a constant distance to the cavity wall of the IHF tool along its circumference in the course of subsequent internal high pressure forming inside an IHF tool. In the course of internal high pressure forming, viewed over the circumference, an approximately uniform forming and stretching of the tube material and thus an excellent material utilization is achieved in this way. This gives rise to many advantages for the IHF process and for the properties of the IHF component. For example, the IHF component that has been produced in this way essentially exhibits a uniform wall thickness.
The preforming of a starter tube section that is present inside the cavity of the tool according to the invention takes place in particular such that at least one of the parts of the tool is displaced relative to at least one of the other parts of the tool. The design features according to the invention for the cavity relate primarily to a final shaping state of the cavity at the end of the forming process, wherein the parts of the tool in particular exhibit the smallest possible distance to each other. The contour of the cavity (or the cavity contour) can be defined as the totality of the geometrical design features of the cavity wall.
Since the cross-sectional circumference of each cavity cross section on the cavity longitudinal axis corresponds exactly to the circumference of the starter tube section, defined, accurate and compression-free forming or preforming of the starter tube section takes place at every point. Indefinite forming is avoided. With regard to the subsequent internal high pressure forming, a starter tube section that has been preformed with the tool according to the invention exhibits an essentially optimal preform and, associated therewith, optimal distribution of the tube material.
It is proposed that the tool according to the invention is preferably a press-based tool having a tool lower part and having a tool upper part that is capable of movement relative thereto. The tool can be opened and closed by raising and lowering the tool upper part. Forming or preforming of a starter tube section that is present inside the cavity is effected by the application of a pressing force, with the tool closed, in conjunction whereby the starter tube section assumes the preform that is predetermined by the contour of the cavity.
A method according to the invention for producing a tool according to the invention for preforming a metallic starter tube section for subsequent internal high pressure forming comprises essentially the following steps:
a.) provision of the geometrical data determining the shape (overall shape) of the IHF component to be produced or alternatively the geometrical data of the cavity of the IHF tool;
b.) determination of the circumference and, if necessary, the cross-sectional shape of the starter tube section to be used, for which purpose, for example, the smallest cross section of the IHF component is considered and, on the basis of its cross-sectional circumference, in particular less 3%, the circumference of the starter tube section is determined;
c.) calculation of the contour of a shaping cavity required for the preforming of the starter tube section by use of guide sections, for which purpose transverse sections are produced initially along the longitudinal axis of the IHF component (or alternatively along the longitudinal axis of the cavity of the IHF tool), and these are then reduced or scaled respectively in respect of their circumference to the calculated circumference of the starter tube section, wherein the guide sections obtained in this way can subsequently be brought together, in order to determine the contour of the cavity therefrom; and
d.) manufacture of the tool with a cavity exhibiting this contour.
This method can include further steps and/or intermediate steps. It is proposed that steps a., b. and c., in particular being automated, are preferably executed with a CAD program or the like, that is to say with the help of computer equipment.
A method according to the invention for producing a tube-like IHF component by internal high pressure forming comprises at least the following steps:
a.) provision of a starter tube section, being in particular a starter tube section having a defined axial length cut to length from a semi-finished product;
b.) preforming and, in particular, kink-free preforming of the starter tube section in a tool according to the invention for preforming; and
c.) internal high pressure forming of the preformed starter tube section in an IHF tool.
The individual steps and the devices or tools used for that purpose are matched to one another. The proposed method can include further steps and/or intermediate steps, of which a number are explained in more detail below.
It is proposed that the starter tube section is preferably pre-bent in a step preceding the preforming operation, essentially without changing any cross section. The bending or pre-bending leads to a tool longitudinal axis having an uneven and preferably complex, although in particular kink-free, spatial course, which corresponds in particular at least approximately to the IHF component to be produced (as illustrated, for example, in EP 0 195 157 B1). The pre-bending also serves to ensure, among other things, that, for the purpose of its preforming, the pre-bent starter tube section can be inserted in line with the shape into the cavity of the tool.
The starter tube section is preferably produced from an aluminum material or a steel material. However, the starter tube section can also be produced from other materials (e.g. brass).
The starter tube section preferably exhibits a circular or oval cross section or a circular or oval cross-sectional shape (in relation to the external shape). The starter tube section can also exhibit other cross-sectional shapes (for example a polygonal shape).
It is further proposed that, in conjunction with internal high pressure forming in the IHF tool, different degrees of circumferential stretching due to plastic material deformation are achieved preferably over the longitudinal axis of the preformed starter tube section, which in particular lie in a range between 3% and 10%. Typically, the circumferential stretching may be greater at the ends of the tube and may have a value of up to 10% at that point, whereas the smaller circumferential stretching in the central sections of the tube should have a value of at least 3%. Forming without heat treatment is possible, in particular in combination with the previously mentioned materials, in the case of circumferential stretching in the aforementioned region. Deformation with a tool according to the invention makes higher circumferential stretching or circumferential enlargement possible to some extent in conjunction with internal high-pressure forming, depending on the nature of the material, than with the procedures that are familiar from the prior art.
The preformed starter tube section is preferably inserted into the cavity of the IHF tool in such a way that it exhibits the same distance to the cavity wall of the IHF tool over the respective cross-sectional circumference at every point on its longitudinal axis, i.e. in such a way that it is surrounded by a gap of uniform width, wherein the distance or the width of the gap may vary depending on the position of the respective cross section on the longitudinal axis. As already described above, approximately uniform forming and thinning due to stretching of the tube material, associated with excellent material utilization, are obtained as a result when observed over the circumference, in conjunction with internal high-pressure forming. The IHF tool can exhibit suitable positioning elements.
The IHF component to be produced is, in particular, a motor vehicle component, in particular such as a body component (for example, an internal reinforcement part) or an axial part (for example, a longitudinal member or a transverse member). There is thus a preference for both a tool according to the invention for preforming and a method according to the invention for producing a tube-like IHF component to be used for producing a motor vehicle component.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.